Copper (Cu) has been used to form the main body of interconnection structures for semiconductor devices, such as silicon semiconductor devices, e.g. system LSI, flash memories, and large-size liquid crystal display devices (LCD) (refer to patent documents 1 to 3 below). Copper (Cu) has higher resistance for electro-migration (EM) or stress-migration (SM) compared to aluminum (Al), and is low in electric resistivity. For example, a technique has been disclosed to form a damascene type copper interconnection structure for silicon system LSIs which are used in Central Processing Units (CPU) (refer to non-patent document 1 below). This technique provides copper interconnections in that copper, which constitutes an interconnection body, is buried inside an interconnection hole, such as trench groove, via, or the like, provided on an interlayer insulating layer made of silicon dioxide (SiO2).    [Patent document 1] Japanese unexamined patent application no. 2005-277390    [Patent document 2] International publication no. WO/2006-025347 A1    [Patent document 3] International publication no. WO/2007-100125 A1    [Non-Patent Document 1] “Semiconductor Device (2nd edition)—Physics and Technology” by S. M. Sze (ISBN4-7828-5550-8 C3055), Oct. 5, 2005, Sangyo Tosho, Co., Ltd., third impression of second edition, P. 355-356.
In single or dual damascene type copper interconnection structures, for example, it is common that the copper interconnection body is provided through a diffusion barrier layer, often referred to simply as “barrier layer” (refer to patent documents 4 to 6 below). The diffusion barrier layer prevents copper from intruding into the interlayer insulating layer so that it prevents a decrease in electric insulating property of the insulating layer. The barrier layer is structured from a thin layer formed from a material, such as tungsten nitride (WN) (refer to patent document 7 below), tantalum (Ta) and nitride or oxide of tantalum (TaN or Ta2O5) (refer to patent document 8 below), or rhenium (Re) (refer to patent document 9 below).    [Patent document 4] Japanese unexamined patent application publication no. H01-202841    [Patent document 5] Japanese unexamined patent application publication no. H11-186273    [Patent document 6] Japanese unexamined patent application publication no. 2001-44156    [Patent document 7] Japanese unexamined patent application publication no. 2000-068269    [Patent document 8] Japanese unexamined patent application publication no. 2004-266178    [Patent document 9] Japanese unexamined patent application publication no. 2007-096241
In recent years, several techniques are disclosed for forming the diffusion barrier layer. For example, as shown in Japanese Unexamined Patent Application no. 2005-277390 and in International Publication no. WO/2007-100125 A1, a technique is proposed for forming a diffusion barrier layer by using a film as a material. The film is made of solid solution or alloy of copper containing a metal element which has a diffusion coefficient higher than the self diffusion coefficient of copper and also features an oxide formation energy lower than that of copper. Further, another technique employing a copper manganese alloy is proposed for forming a barrier layer made of manganese dioxide (MnO2)(refer to patent document 10 below). In this technique, the barrier layer is formed on a layer containing at least one metal element selected from a group of silver (Ag), zinc (Zn), cadmium (Cd), tin (Sn), aluminum (Al), chromium (Cr), palladium (Pd).    [Patent document 10] Japanese unexamined patent application publication no. 2007-96241
Additionally, a technique is disclosed for forming a diffusion barrier layer made from manganese silicon oxide, MnSiO3 or MnSi3O5, using a copper layer containing manganese (Mn) as an alloying material by heat oxidation treatment (refer to patent document 1). By looking at the composition of the manganese oxide, which constitutes the conventional diffusion barrier layer, compositional ratios of oxide to manganese are 3 for MnSiO3 and 5 for MnSi3O5. Moreover, a technique for providing a manganese oxide layer on an upper surface of copper constituting the copper interconnection body is disclosed. The manganese oxide layer is provided as a barrier layer for preventing copper oxidation. The barrier layer for preventing copper oxidation is made from MnO2 and is formed on the upper surface of the copper interconnection body (refer to patent document 11 below). In any of the above-mentioned barrier layer, the compositional ratio of oxygen to manganese, in the manganese oxide, is not less than 2.    [Patent document 11] Japanese unexamined patent application publication no. H11-186273
There is an advantage in forming easily a diffusion barrier layer using materials, such as a thin layer made of solid solution or ally of copper containing metal element. The metal element has a diffusion coefficient greater than the self diffusion coefficient of copper and has an enthalpy of oxide formation lower than that of copper. However, a problem still remains in that the copper interconnection having sufficient adhesiveness can not be stably formed on the diffusion barrier layer.
It is found that in the case where the interconnection body is formed on a diffusion barrier layer made of manganese oxide, the adhesiveness between the copper interconnection body and the diffusion barrier layer can not be secured sufficiently if the compositional ratio of oxygen against manganese in the manganese oxide is 2 or higher. This is because the four electrons involved in manganese bond are all used up for bonding with oxygen atoms and therefore there remains no electron for interacting with copper atoms.
The present invention is proposed in view of the above aforementioned problem. An objective of the present invention is to provide a copper interconnection, semiconductor device and method for forming the copper interconnection that are capable of significantly improving the adhesiveness between the diffusion barrier layer and the copper interconnection body.